Laboratory‐scale Investigation of the Influence of Ageing on the Performance and Sensitivity of an Explosive Containing ϵ‐CL‐20

Abstract

The performance and sensitivity of aged composite explosives based on the epsilon polymorph of hexanitrohexaazaisowurtzitane (ϵ‐CL‐20) have been evaluated with the laser‐induced air shock from energetic materials (LASEM) technique using only milligram quantities of material. The LASEM results demonstrated reduced explosive performance (i. e., lower estimated detonation velocities) and higher sensitivity to ignition with increasing ageing. Chemical analysis of the explosive formulation subjected to ambient and accelerated aging was conducted to help understand the LASEM results. The Fourier Transform Infrared (FTIR) spectra revealed no evidence for conversion to lower‐energy polymorphs. Based on the desorption gas chromatography/mass spectrometry (D‐GC/MS) results, the observed decrease in performance and increase in sensitivity for the explosive powder aged at 100 °C (relative to ambient and 70 °C aging) have been attributed to changes related to solvent inclusions in the molding powders.

Ultra‐High Fidelity Laser‐Induced Air Shock from Energetic Materials

“…The results presented herein are in conflict with the published methods [5][6][7][8][9][10][11][12][13][14] for the LASEM technique, mainly: 1) transformation of the spatiotemporal data to velocitytime space, 2) use of the fifth-order polynomial for representation of the data, and 3) extrapolation of the fifth-order polynomial outside the experimentally measured dataset bound. However, a measurable difference was found between the baseline adhesive and HE materials, suggesting that the HE materials do indeed contribute to the laser-generated plasma, but outside the bounds of the length and time scales presented herein.…”

“…The target slides are oriented parallel to the optics table and mounted to a three-axis translational stage to permit laser ablation across the entire HE sample. Laser-pulse energy and spot size are chosen to replicate, as closely as permissible, the experimental parameters published by Gottfried [5][6][7][8][9][10][11][12][13][14]. The target is raised such that the laser focal point falls beneath the target surface as prescribed by Gottfried [6].…”

“…More recently, Gottfried et al published a similar technique possessing the capability to predict detonation-performance parameters of new and novel HE and/or HE formulations by demonstrating an empirically based correlation between detonation-performance parameters and the external shock wave velocity generated by laser ablation of sub-mg quantities of HE. The technique is referred to as LASEM: laser-induced air shock from energetic materials, and its novelty is challenging the axiom that energetic-material-performance characterization is unable to be completed at the sub-mg scale [5][6][7][8][9][10][11][12][13][14]. In brief, a small quantity (< 40 mg) of a target HE is spread onto a piece of double-sided adhesive that is adhered to a glass microscope slide.…”

“…The characteristic laser-induced shock velocity has been shown to correlate with multiple performance metrics, including: 1) heat of combustion, 2) detonation energy, 3) detonation pressure, and 4) published theoretical maximum density (TMD) bulk-detonation velocity for numerous HE materials characterized. Ultimately, it is claimed that linear calibration curves generated from these correlations permit an explosive-performance characterization for novel HE or HE formulations [5][6][7][8][9][10][11][12][13][14].…”

The Role of Pentaerythritol Tetranitrate (PETN) Aging in Determining Detonator Firing Characteristics

“…However, there still exist important gaps in predicting its behavior in standard commercial detonators over long periods of time. In general, the analysis of aging characteristics of explosives and their influence on initiation behavior is an important topic of interest [8,9,10]. Though small-scale studies have been performed on specific detonator systems with isolated batches of material, what is missing is a large statistically-significant study focusing on PETN aging characteristics -such as powder coarsening -and their influence on detonator performance.…”